Moving coil electromagnetic vibrators

ABSTRACT

In an electromagnetic vibrator a stationary magnet affords an annular or part annular airgap containing a moving conductor unit capable of vibratory movement about the axis secured to an output member to transmit torsional vibration to a load. Alternating current is passed through the conductor unit in directions substantially parallel to its axis. In one embodiment provision is made for vibratory movement both longitudinally along the axis and angularly about the axis.

United States Patent inventors Peter Grootenhuis London; James Walter Gearing, St. Leonards-on- Sea, Essex, both 01, England Appl. No. 831,925 Filed June 10, I969 Patented July 6, 1971 Assignee Derfltron Limited London, England Priority June 11, 1968 Great Britain 27658/68 MOVING COIL'ELECTROMAGNETIC VlBRATORS 7 Claims, 11 Drawing Figs.

US. Cl 310/27,

v 3 10/36 in. C1. H021: 33/18 Field ol'Search 31 /35,

115; 179/1155 OUC; 310/13, 27, 3639; 335/221,222,23I

Anderson et a1. IBM TECHNICAL DISCLOSURE BUL- LETlN, Linear Actuator," 4/61, Vol. 3, 11 ,pp. 3 & 4.

Primary Examiner-D. F. Duggan Attorney-Watson, Cole, Grindle & Watson ABSTRACT: In an electromagnetic vibrator a stationary magnet affords an annular or part annular airgap containing a moving conductor unit capable of vibratory movement about the axis secured to an output member to transmit torsional vibration to a load. Alternating current is passed through the conductor unit in directions substantially parallel to its axis. In one embodiment provision is made for vibratory movement both longitudinally along the axis and angularly about the axis.

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SHEET 3 OF 6 INVENTOR PETER Gnoo'rcununs James W. Gamma PATENTEDJUL BIB?! 3.591.815

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INVENTOR PII'IR GROOYENHUIS James NGemama ATTORNEY;

PATENTEU JUL SIB?! 3591.815

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INVENTOR QR GRooTerm [S W. Guam PATENTED JUL slsn 3591.815

SHEET 6 BF 6 INVENTOR PETIR Glmveunuas BY James W. Gimme ATTORNEYS MOVING COIL ELECTROMAGNETIC VIBRATORS This invention relates to electromagnetic vibrators. According to the present invention an electromagnetic vibrator includes a stationary magnet affording an annular or part annular airgap, a moving conductor unit suspended in the airgap so as to be capable of vibratory movement about its axis, means for passing alternating current through the conductors of the conductor unit in a direction substantially parallel to the axis, and an output member secured to the conductor unit to transmit torsional vibration to a load.

In a preferred form of the invention the inner pole piece is of one polarity and the whole of the outer pole piece is of the opposite polarity.

The moving conductor unit may comprise a number of separate conductors lying parallel to one another and to the axis of the unit, and connected at their ends to bus bars which lie outside the magnetic field and through which current is fed to the conductors. All the conductors may be connected between a single pair of bus bars or combined to form an integral tube. Alternatively a number of bus bars may be provided at each end each connected to a group of conductors or a section of a tube, the bus bars being connected by external connections so as to connect the groups of conductors in series with one another. Such an arrangement may well be desirable in order to facilitate matching the impedance of the moving conductor unit to the output of an alternating supply.

The suspension of the moving conductor unit may be effected in various ways. It may include a central pivot. Alternatively or in addition it may comprise a number of beams each connected at one end to the conductor unit or output member and at the opposite end to a stationary part. Such connections may be made by means of couplings of the type including an annular bush or rubber or like resilient material interposed between inner and outer members each affording a surface of revolution about the axis about which the parts of the coupling turn relatively to one another. Preferably each such beam extends in a direction having at least a radial component, the axes of the pivots being substantially parallel to that of the airgap.

In a further form of the invention an electromagnetic vibrator includes a stationary magnet affording an annular cylindrical airgap between inner and outer pole pieces, and a moving conductor unit suspended in the airgap so as to be capable of vibratory movement both longitudinally along the axis and angularly about the axis, and affording circuits through which currents can be passed generally circumferentially to produce the former mode of vibration and generally longitudinally to produce the latter mode of vibration.

The invention may be put into practice in various ways but certain specific embodiments will be briefly described by way of example, with reference to the accompanying diagrammatic drawings in which: 7

FIG. 1 and 2 are respectively a sectional elevation through the axis, and a plan view, of one form of electromagnetic vibrator,

FIG. 3 is a view similar to FIG. 1 of a modified arrangement having a slotted inner pole piece,

FIG. 4 is a sectional plan on the line 4-4 of FIG. 3.

FIG. 5 is a perspective view of a vibrator having a part-annular airgap,

FIGS. 6 and 7 are respectively a sectional plan and a sectional elevation of the vibrator of FIG. 5,

FIG. 8 is a sectional elevation indicating an arrangement of crossed beams for suspension,

FIG. 9 is a sectional elevation of a vibrator providing combined longitudinal and angular vibrations along and about its axis, and

FIGS. 10 and 11 are perspective views respectively of two forms of beam or link for the suspension of the vibrator of FIG. 9.

being shaped to leave between them a narrow annular airgap l4.

Suspended in the annular airgap is a moving conductor unit 15 in the form of a hollow cylinder made up of a large number of conductors 16 extending parallel to the axis between a pair of annular bus bars 17 and 18 lying respectively above and below the airgap. The support 19 for the moving coil is rigidly secured to the skirt of an output member 20 comprising a disc 21 with the skirt 22 depending from its periphery, a boss 23 depending from its center and a number of radial webs 24 connecting the boss to the skirt.

The output member is suspended on the pot magnet so as to be capable of vibrating about the axis. For this purpose it may have a center pivot bearing 25, or a central resilient coupling connecting the boss to the inner pole piece of the magnet. In addition a number of radial beams 30 are situated under the disc of the output member and each having its inner end connected by a resilient coupling 31 to the disc, whence it extends out through an opening in the skirt and has its outer end connected by a similar coupling 32 to an anchorage secured to the outer pole piece of the magnet.

Each resilient coupling is of the type comprising a hollow cylindrical bushing of rubber or like resilient material radially compressed between inner and outer sleeves, and preferably bonded to them. Conveniently, as shown, the outer sleeve fits into or is afforded by the end of the beam, while the inner member is secured to a post fixed to the outer pole piece or the output member.

The axes of the bushings lie parallel to that of the vibrator, and the beams 30 are preferably rigid, the bushings being re lied upon to accommodate the whole of the relative angular movement between the beams and the parts to which they are connected, as well as the very small relative movement in a radial direction.

Each moving bus bar 17 or 18 is connected to a fixed bus bar 41 or 42 by means ofa number of conductors 43 each of which is of such form, for example braided, as to flex readily to allow the angular movement of the moving bus bars. The fixed bus bars are connected to an external AC supply in any convenient way, for example one or more conductors 44 from the lower fixed bus bars 42 may extend up through a bore 45 to the outer pole piece.

Assuming each bus bar is in the form of a complete ring all the longitudinal conductors of the moving conductor unit will be connected in parallel and current will pass through them in the same direction when the bus bars are connected respectively to the terminals of an AC oscillator or generator. As indicated above the bus bars are outside the magnetic field since otherwise current flowing from a flexible connector, round one portion of the bus bar in one direction and the other portion in the other direction, would produce a vibratory tilting force on the bus bar.

Alternatively the conductors of the conductor unit may be divided into groups each connected between a pair of part annular bus bars, and the upper bus bar of one group is connected through an external conductor such as the conductor 45 to the lower bus bar of the next group so as to connect the conductors in series. This will generally facilitate matching the impedance of the complete conductor unit to the output'of the generator.

' In a further embodiment shown in FIGS. 3 and 4 the inner pole piece is provided with a number of radial slots 50 and a central depression 51. to receive the boss 52 and webs 53 of the output member which extend much lower than in the first construction. Thus the lower edge of each web at its outer end is substantially level with the lower end of the moving coil.- The radial slots diverge outwards so as to allow the required amplitude of angular vibration of the output member and its webs, and the conductors of the conductor unit, are arranged in groups with gaps opposite the slots, the outer pole ring also being slotted at 54 in order to concentrate the magnetic flux in the portions of the circumference occupied by the groups of conductors.

In other respects the construction of FIGS. 3 and 4 is similar to that of FIGS. 1 and 2.

In a further embodiment shown in FIGS. 5 to 7 the airgap is of part annular form, comprising only two opposite part cylindrical portions 60, which are symmetrical about the axis. Thus the two arcuate or part-cylindrical portions 61 of the conductor unit may be connected by a pair of flat plates 62, the inner pole piece 63 and outer pole piece 64 having similar pairs of flat sides 65 and 66 parallel to one another adjacent the part cylindrical faces presented to the airgap. In this case the suspension system in addition to beams like those of FIGS. 1 to 4, above the airgap, may include beams 67 below the airgap extending beneath the flat plates 62 and connecting anchorages 68 on their outer faces with anchorages 69 carried by the flat faces of the inner pole piece. In addition it may include a central bearing or rubber bush coupling 70.

In the embodiments described, the center pole piece is of one polarity and the outer pole piece is wholly of the opposite polarity. Thus in the embodiment last described the field magnet is generally of E-shape with the center limb of one polarity and both outer limbs of the opposite'polarity. In a further alternative embodiment the outer pole pieces may be of opposite polarity, opposite ends of the center pole piece also being of opposite polarity. The outer pole pieces may then form part of a U-shaped magnetic circuit incorporating windings or permanent magnets, while the inner pole piece may either incorporate a permanent magnet or a winding or may be of a high permeability material magnetized solely by the outer pole pieces. In such arrangements the current must, of course, flow in opposite directions in the conductors respectively in the two portions of the airgap. For this purpose they may, if desired, be wound in the form of a coil.

FIG. 8 shows diagrammatically a further form of suspension incorporating pairs of beams 72 extending diametrically and diagonally past one another. This arrangement reduces the angular movement required in each rubber bush coupling.

In a further embodiment of the invention shown in FIGS. 9 to 11 the vibrator is constructed so that the moving conductor unit can be vibrated either longitudinally parallel to the axis or angularly about the axis, or both at the same time.

The construction may follow generally any of the embodiments already described, with certain modifications. In the first place the moving conductor unit has two sets of conductors in one of which 80 the conductors extend longitudinally in order to give angular vibration as in the embodiments already described, while in the other 81 they extend circumferentially to form one or more coils as in conventional moving coil vibrators where the movement is purely longitudinal. For example the longitudinal conductors may be arranged on the inner face of a tubular former or support 82 while the circumferential conductor may be wound round the outside of the support or former.

In each case the conductor may comprise a hollow tube through which cooling fluid can be passed. In addition further tubes for the circulation of cooling fluid may be incorporated in the support between the two coils, for example as set forth in the present applicants British Pat. No. 1451824.

The two sets of conductors are connected to the stationary structure by separate flexible connectors (not shown) so that alternating currents can be supplied to them independently. Thus the amplitudes of the two modes of vibration may be separately varied so that either mode will predominate and in addition the frequencies or wave forms of the currents supplied to the two circuits may also be independently varied. For example the output table may be given a slow sinusoidal angular vibration accompanied by a random vibration in the longitudinal direction over a wide frequency range.

In .order to accommodate the two modes of vibration each of the suspension beams or links is arranged so that the rubber bush 86 at the inner end has its axis parallel to that of the vibrator, while the rubber bush 87 at the outer end has its axis perpendicular or tangential to that of the vibrator. The suspension link 85 is formed from a comparatively thin strip which is twisted at an intermediate point so that its outer end portion 88 lies in a vertical plane and its inner end portion 89 in a horizontal plane. Thus the movement about an axis perpendicular to that of a bush can be taken partly by compression of the bush itself and partly by bending of the link. At least three suspension links are provided so as to center the conductor unit in the airgap.

The bushes secured to the outer pole piece may be given a pretwist or bias so as to tend to lift the suspension unit to take the whole or part of the weight of a test piece. In addition a spring 90 can be provided between the center of the table and the center of the inner pole piece for the same purpose. This may surround a bearing '91, conveniently of a plastics such as p.t.f.e. allowing both longitudinal and angular movement.

The control'link may take various forms. Thus in one arrangement the inner member of the outer bush, having its axis horizontal and tangential, has each end secured to one of two links each twisted as already described while the inner end of each link is secured to the inner member of one of two separate rubber bushes having their outer members secured to the table near its center. In analternative arrangement indicated in FIG. 10 each link is forked, with two limbs 93 secured as described above to opposite ends of the bush at the outer end, while the stem 94 is secured to the center member of a bush near the center of the output table.

In a further alternative illustrated in FIG. 11 a rigid link'95 may have at one or each end two rubber bush couplings 96 and 97 with their axis at right angles so as to permit both modes of movement without relying on any flexing of the link.

We claim:

1. An electromagnetic vibrator for providing torsional vibration about an axis, comprising;

a stationary field magnet structure including an inner pole piece of one polarity and an outer pole piece of the'opposite polarity,

said inner and outer pole pieces forming an annular airgap therebetween symmetrical with respect to said axis,

an output member mounted to said field magnet structure for transmitting said torsional vibration to a load,

a conductor unit movably positioned in said airgap and fixed to said output member and including a plurality of electrical conductors extending substantially parallel to said axis, at least one end conductor electrically interconnecting said electrical conductors,

at least one bus bar mounted to said field magnet structure,

and

flexible connectors connecting said conductors to said at least one bus bar.

2. A vibrator as claimed in claim 1 in which there are a number of end conductors and bus bars, each endconductor connected to a group of electrical conductors, said flexible connectors connecting said groups of electrical conductors in series with one another.

3. A vibrator as claimed in claim 1 in which the mounting of said output member includes a central pivot.

4. A vibrator as claimed in claim 1 further comprising mounting means for mounting said output member to said field structure, said mounting means includes a number of beams each connected at one end to said output member and at the opposite end to said field structure.

5. A vibrator as claimed in claim 4 in which the connections of the beams are made by means of couplings of the type including an annular bush of rubber or like resilient material interposed between inner and outer members each affording a surface of revolution about the axis about which the parts of the coupling turn relatively to one another.

so as to be capable of vibratory movement both longitudinally along the axis and angularly about the axis, whereby electrical energization of said additional electrical conductors produces the former mode of vibration and electrical energization of said electrical conductors produces the latter mode of vibration. 

1. An electromagnetic vibrator for providing torsional vibration about an axis, comprising; a stationary field magnet structure including an inner pole piece of one polarity and an outer pole piece of the opposite polarity, said inner and outer pole pieces fOrming an annular airgap therebetween symmetrical with respect to said axis, an output member mounted to said field magnet structure for transmitting said torsional vibration to a load, a conductor unit movably positioned in said airgap and fixed to said output member and including a plurality of electrical conductors extending substantially parallel to said axis, at least one end conductor electrically interconnecting said electrical conductors, at least one bus bar mounted to said field magnet structure, and flexible connectors connecting said conductors to said at least one bus bar.
 2. A vibrator as claimed in claim 1 in which there are a number of end conductors and bus bars, each end conductor connected to a group of electrical conductors, said flexible connectors connecting said groups of electrical conductors in series with one another.
 3. A vibrator as claimed in claim 1 in which the mounting of said output member includes a central pivot.
 4. A vibrator as claimed in claim 1 further comprising mounting means for mounting said output member to said field structure, said mounting means includes a number of beams each connected at one end to said output member and at the opposite end to said field structure.
 5. A vibrator as claimed in claim 4 in which the connections of the beams are made by means of couplings of the type including an annular bush of rubber or like resilient material interposed between inner and outer members each affording a surface of revolution about the axis about which the parts of the coupling turn relatively to one another.
 6. A vibrator as claimed in claim 5 in which each beam extends in a direction having at least a radial component, the axes of the couplings being substantially parallel to that of the airgap
 7. An electromagnetic vibrator as claimed in claim 1 wherein said conductor unit further includes additional electrical conductors extending substantially perpendicular to said vibration axis, said conductor unit is suspended in the airgap so as to be capable of vibratory movement both longitudinally along the axis and angularly about the axis, whereby electrical energization of said additional electrical conductors produces the former mode of vibration and electrical energization of said electrical conductors produces the latter mode of vibration. 